This invention relates to an automatic assembly machine and, more particularly, to an automatic assembly machine of the type which includes a rotary motor operable to drive an elongated spindle. The free end of the spindle carries a driver which is operable to tighten a threaded fastener such as a screw or a nut during rotation of the spindle.
An assembly machine of this general type is disclosed in Dixon U.S. Pat. No. 2,989,996. In that machine, a torque-responsive clutch is interposed in the drive between the motor and the spindle. When the fastener tightens and torque of a predetermined magnitude is imposed on the spindle, the clutch automatically disengages to interrupt the drive to the spindle and avoid overtorquing of the fastener.
It is desirable to drive the fastener at a high speed in order to achieve fast cycle times. During final tightening of the fastener, however, it is desirable to reduce the driving speed in order to better control the magnitude of the final torque applied to the fastener. In prior automatic assembly machines, there either is no provision for reducing the driving speed of the fastener just prior to final tightening without momentarily stopping rotation of the driver or, if such provision is made, a costly and complex electronic control is required.